1. Field
The present invention relates to controlled radical polymerization processes, reaction products of such processes, and compositions containing such reaction products. More particularly, the invention relates to a process of controlled radical polymerization of acrylic and/or methacrylic acid monomers employing a defined order of introduction of the reactants, and/or a specific set of reaction conditions.
2. Brief Description of Related Technology
Demand for increasingly efficient ways to produce polymers continues. Controlled radical polymerization (“CRP”), including single-electron transfer living radical polymerization (“SET-LRP”) and atom transfer living polymerization (“ATRP”), is a process which produces various polymer products, in high yield, with functional, non-terminated ends, with high molecular weights, and with a low polydispersity index. Thus, CRP has been employed to design a variety of polymer products. However, these CRP processes typically require the use of solvents that are toxic and/or are difficult to remove from the final products. This creates concerns about the safety and purity of the polymers.
Previous CRP polymers have shear modulus values which are less than desirable for many applications. Moreover, CRP polymers can be difficult to modify for use in applications requiring flexibility, thermal resistance, fluid resistance and other desirable physical and chemical properties. In particular, previous CRP polymers often have a broad molecular weight distribution indicating that the polymer produced is not actually a single polymer, but instead is a blend of numerous polymers. The physical properties of broadly distributed polymer blends are different from those of narrow distributions. The production of a blend of polymers can lead to inhomogeneity in polymer structures and difficulty in processing. For example, small amounts of high MW polymer chains disproportionally affect the viscosity and can be difficult to process.
Thus, there exists a need for a CRP polymer process that allows (a) better control of polymerization exotherm; (b) reduced viscosity of polymerization solutions; and (c) better yields of recycled solvents, increases the uniformity in structure and properties of the polymers produced, and does not employ toxic solvents that are difficult to remove from the final polymer product.
ATRP provides a method to build polymers. Typically, ATRP can be performed on a narrow range of monomers with a narrow range of initiators. Also, ATRP is typically catalyzed with a metal in the +1 (or M+1), or other lower oxidation state, such as a Cu(I) salt catalyst. As the polymerization process is slow, high concentrations of the catalyst are needed to drive the reaction as are high temperatures which must be maintained for a prolonged period of time. Though functional ends are desirable for the final product polymer, an ATRP catalyst can be unstable and promote termination concomitant with formation of non-functionalized end groups.
Thus, ATRP generally gives material containing some non-functionalized polymer with unreactive end groups. As a result, a typical polymer produced by ATRP may contain in the region of 10-15% of the chain ends terminate to provide material with less desirable mechanical and material properties and characteristics. Both the molecular weight and the polydispersity index of the product diverge from theory by the premature termination of the polymer ends, which often results in poor rheological control and impracticability in various applications and uses. Thus, the lack of control of the ATRP process results in polymer products with structural defects, less desirable features, and less predictable characteristics. In addition, Cu(I) salts are unstable in air and require care in handling.
There exists a need for a method of controlled radical polymerization that allows for better control of the structure, composition, and properties of the polymer to be produced.